Artuğer, Fırat; Özkaynak, Fatih

In recent years, the need for secure cryptographic keys for various purposes has been constantly increasing. One of these areas is undoubtedly image encryption. In this study, a new key generation algorithm has been developed for use in image encryption algorithms. The proposed generator has a hybrid structure based on the chaotic sine map and the SHA-3 algorithm. It is aimed to produce strong keys by using the benefits of these two structures. To do this, first, bit sequences of the desired length are generated using the basic parameters of the sine map. Then, bit sequences of the same length are obtained using the SHA-3 algorithm. These two bit sequences are then subjected to an XOR operation to generate key values ​​of the desired length. With this structure, 3 different bit sequences of 1 million length were produced. All of these bit sequences successfully passed NIST SP 800 − 22 tests. This key value obtained in this study has been successfully applied to a new image encryption algorithm. The results of the study demonstrate that the proposed algorithm meets important cryptographic criteria such as information entropy, correlation-histogram analysis, NPCR, and UACI values. In addition, the simple and fast structure of the algorithm in key generation was the most important difference from other studies.

AtıfScopus3·OpenAlex2

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Artuğer, Fırat

The most used approach for data encryption is block cipher. One of the most important structures for block cipher algorithms is undoubtedly s-boxes. The s-box structure used in the AES algorithm contains 256 values. Therefore, obtaining powerful s-boxes is a rather difficult search problem. Because the search space is very large (256!). In this study, a new method based on squirrel search algorithm (SSA) is proposed to overcome this problem. The proposed method is displacement-based. In an s-box taken at the entrance, stronger s-box structures are sought by changing the location of the elements. The most important innovation in this study is that the elements to be displaced in the s-box were selected with the positioning states of the SSA. The chaotic Gompertz map was used for the initial population. Four different s-boxes were produced with the method developed thanks to the effective positioning states of SSA. As the fitness function, the nonlinearity value, which is the most important evaluation criterion of an s-box structure, was used. The proposed four s-box structures increased up to 110 nonlinearity values after only 4500 iterations. Here, it has been shown that the algorithm can be effective in all s-boxes by generating four different s-boxes. Considering these results, it has been determined that the proposed method gives more effective results than most methods in the literature.

AtıfScopus1·WoS1·OpenAlex2

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Artuğer, Fırat

With today's developing technologies, the need for new image encryption algorithms to encrypt images is inevitable. In this study, an innovative image encryption algorithm is proposed. The proposed algorithm first XORs each layer of the image with a unique and strong new key. Each layer is then subjected to a random permutation process. Each of the encrypted layers obtained here is finally passed through a new s-box structure with a high nonlinearity value. After these processes, all layers are combined to obtain an encrypted image. Thus, XOR and s-box confusion meet the criteria, while random permutation meets the diffusion criteria. In this study, both key and s-box structures were originally obtained with a chaotic Gaussian map. The outputs of the chaotic map were converted into bit sequences and five different sequences with a length of 1 million were obtained. All these arrays have successfully passed all NIST SP 800-22 tests. On the other hand, the proposed s-box structures surpassed many studies with nonlinearity values of 108, 108.5, and 108.75. The images were successfully encrypted with the proposed algorithm, and the encrypted images successfully completed tests such as NPCR-UACI, information entropy, histogram analysis, and correlation analysis. It is thought that this study will make many contributions to the fields of s-box development, random number generation, and image encryption.

AtıfScopus3·OpenAlex3

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Artuğer, Fırat; Özkaynak, Fatih

One of the successful practical applications of chaos theory and nonlinear dynamics is chaos-based cryptology studies. In this study, a new chaotic system is proposed. The proposed chaotic system generator model has a simple algorithmic structure. In addition to, generated chaotic systems have rich dynamics. It has been examined whether this system has potential advantages, especially for information security applications. As a result of the analysis and experimental studies, it is seen that the study makes many contributions to the literature. The simple mathematical generator structure has the potential to reduce computational complexity, which is an important problem for cryptology applications. One of the most comprehensive studies has been realized for chaos-based substitution box designs. 70,000 different substitution box structures have been generated. It has been known that the highest nonlinearity value that can be achieved for designs that transform chaotic system outputs into substitution box structures is 106.75 today. It has been shown that this value may be higher. The new highest nonlinearity value is calculated as 107. Side channel analysis has been examined for substitution box structures with the highest nonlinearity value among the substitution boxes generated in the study. Analysis results show that the proposed new substitution box structures may have an advantage for application-oriented attacks. Among the generated substitution box structures, 289 substitution box structures with a nonlinearity value of 106 and above are presented as a public dataset for researchers to use. In addition, 3 different random sequences with a length of 1 million-bit were produced with the proposed map, and the NIST SP 800–22 test was applied. Test results for all datasets were successful. In this way, the proposed map can also be used as a random number generator.

AtıfScopus13

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Artuğer, Fırat; Özkaynak, Fatih

Symmetric encryption approaches are generally used for data encryption. One of the basic requirements for symmetric encryption algorithms to provide security is strong s-box structures. Because s-box is a nonlinear unit in these encryption algorithms and provides the requirement called confusion. In this article, a new technique is developed to produce effective s-boxes like the 16*16 s-box structure used in the AES algorithm. In the proposed method, the sine cosine algorithm (SCA), one of the recently developed optimization algorithms, is used. SCA is a suitable option for generating strong s-boxes because of its strong randomness and ease of implementation. The proposed method first uses a logistic map to generate the initial population. Then, the nonlinearity value is optimized with the help of the sine cosine algorithm. The proposed method reaches the highest nonlinearity value (112) by relocating 126 values in the s-box structure produced initially. Looking at the results, it is seen that the proposed method gives better results than other optimization-based s-box creation methods. This new method has significant potential to improve the security of symmetric encryption algorithms and make data encryption processes stronger.

AtıfScopus19·WoS22·OpenAlex24

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Artuğer, Fırat

S-boxes are very important structures for encryption algorithms. For S-boxes to be strong, they should not be as linear as possible. Obtaining an S-box with high nonlinearity is a difficult problem. For this reason, it has attracted the attention of researchers for many years. In this study, cellular automata logic was used to overcome this problem. A chaotic tent map was used for the initial population. Then, in this weak S-box, the elements were replaced with their neighbors, and the nonlinearity value was checked. When this value increased, the S-box was transferred to the next generation. With the proposed algorithm, an S-box structure with a nonlinearity value of 110.5 was obtained. This value surpasses most studies in the literature. In addition, it has been proven because of the analysis that the proposed S-box also provides other performance criteria.

AtıfScopus6·WoS8·OpenAlex7

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Artuğer, Fırat

Cryptography aims to design algorithms for the protection of important data transmitted over unsecured networks. These algorithms encrypt the data and render it incomprehensible even if it is captured by enemies. Today’s data encryption standard is the AES algorithm. The most important and nonlinear unit in the AES algorithm is the s-box structure. The S-box provides the mixing process in the algorithm, that is, the confusion. An s-box structure with a high nonlinearity value greatly increases the security against various attacks. Therefore, s-box is of vital importance in an encryption algorithm. When we look at the literature, chaos-based s-box structures are frequently used. However, the nonlinearity value of s-boxes produced with chaos is low. In this article, a new, fast, and very simple method is proposed to increase the nonlinearity value of chaos-based s-box structures. In the proposed method, the nonlinearity value is calculated by changing the places of the elements respectively. When the nonlinearity value increases, the s-box is updated, and the next element is passed. In this way, many iterations are not looked at in vain. This saves a lot of time. As a result of the analysis, it has been proven that the s-box structure obtained by the proposed method is cryptographically strong and has a high nonlinearity value. It is thought that the proposed method will provide many advantages for future cryptography applications.

AtıfScopus9·WoS7·OpenAlex8

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Artuğer, Fırat

Substitution boxes are very important for cryptographic structures. But getting an 8-bit strong s-box is a difficult problem. To address this problem, a new approach is proposed in this study. DNA chains are used in the proposed approach. First of all, a weak s-box is obtained with the help of a chaotic map. Then, a DNA chain is formed with the same chaotic map. In this study, 2000-long DNA chains were produced. Then, two random values consisting of four components are determined from these DNA chains, and these values are addressed to the s-box structure. By changing the places of these values, the s-box structure is improved up to a certain iteration. In this study, 10,000 iterations were examined, and three different strong s-boxes were obtained by using three different DNA chains. The nonlinearity values of these s-box structures were observed as 110.25, 110.5, and 110.75, respectively. The proposed study has proven to work effectively with effective results in three different chains. In addition, it has been proven as a result of the analysis that the proposed s-box structures also have other cryptographic features. The proposed algorithm has surpassed many s-box generation philosophies in the literature. In addition, the proposed algorithm will provide serious gains to cryptographic structures that will be developed in the future.

AtıfScopus21·WoS22·OpenAlex24

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Artuğer, Fırat; Özkaynak, Fatih

The main reason that makes chaos theory attractive for cryptology studies is the unpredictable nature of chaotic systems. However, the fact that the statistical and cryptographical properties of cryptographic primitives based on the values obtained as a result of the electronic circuit implementation of a chaotic system are not as good as the designs based on mathematical transformations has occupied the agenda of researchers. One of the most striking examples of this problem in practical applications is substitution-box (s-box) structures. While the nonlinearity value is 112 for s-box designs based on mathematical transformations, this value is in the range of 103–106.75 for s-box designs based on random (chaotic) transformations. Thanks to the post-processing algorithm proposed in this study, it has been shown that this problem can be resolved and the nonlinearity values of chaos-based s-box structures can be improved up to 111.5. It is thought that the proposed post-processing algorithm may have various potential contributions not only to improve the nonlinearity criterion of s-box structures but also to other information security applications such as cryptographic random number generators in future studies.

AtıfScopus19·WoS13·OpenAlex16

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Artuğer, Fırat

There are two basic requirements for symmetric encryption algorithms. The first of these is diffusion. The second and most important is confusion. In these algorithms, this requirement is usually met by s-box structures. Therefore, s-box structures must be strong. So, a cryptographically good s-box will make the encryption algorithm difficult to crack. However, obtaining a strong s-box is a rather difficult problem. In this study, Josephus circle logic is used to solve this problem. Initially, with a random s-box structure, the elements are replaced according to their Josephus positions, and the s-box is made stronger. In the proposed algorithm, according to the Josephus logic, the elements that kill each other are replaced and this process continues until one element remains. The last 30 surviving elements are replaced with all elements. In this way, three different s-boxes were obtained. In two of them, the nonlinearity value was 110.5, and in one of them, the nonlinearity value was 110.75. Fixed points in the proposed s-box structures were identified and eliminated. In addition, it has been proven because of the analysis that the obtained s-box structures also meet other cryptographic requirements. In addition to leaving behind most studies in the literature, the proposed method will also provide strong s-box structures for encryption algorithms to be built in the future.

AtıfScopus15·OpenAlex12

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Artuğer, Fırat

Encryption provides security in cases such as storing confidential information or transmitting it over a network. Today, block cipher algorithms are generally used for encryption. Undoubtedly, one of the most important units of block cipher algorithms to ensure confidentiality is substitution box (s-box) structures. Because s-boxes are nonlinear structures, making the algorithm resistant to differential cryptanalysis. Therefore, the higher the nonlinearity value of the s-box, the stronger it will be. In this study, a new algorithm is proposed to generate s-boxes with high nonlinearity value. In the proposed algorithm, Lorenz and Chua systems, which are 3D chaotic maps, are used for the initial population. The s-boxes produced with these chaotic maps were then increased to 110.5 using the whale optimization algorithm (WOA). WOA is one of the important optimization algorithms developed in recent years and was used for the first time in s-box production in this study. Looking at the results of the analysis, the proposed method has outstripped most of the other existing studies, thanks to effective 3D chaotic maps and WOA.

AtıfScopus44·WoS38·OpenAlex45

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Artuğer, Fırat; Özkaynak, Fatih

In today’s digital world, effectively transferring data from one point to another is an important problem. For this reason, the development of various new compression algorithms and making existing solutions more effective are examined in detail by researchers. In this study, a new method is proposed to improve the performance of JPEG algorithm. The proposed method includes an approach based on chaotic systems. Chaotic systems contain a strong entropy source. This powerful source of entropy has strong practical applications in obtaining statistically robust random values. In this study, a method is proposed to obtain quantization tables effectively by taking advantage of this potential of chaotic systems. The obtained results showed that the compression performance can be increased at the same quality factors. The proposed approach has been tested on the whole slide image (WSI) dataset. Looking at the analysis results, an average of 2.43% higher accuracy was achieved compared to the JPEG algorithm. It is thought that these results can provide an advantage especially in transferring high-dimensional images such as the DICOM standard, where the JPEG algorithm is used in practical applications.

AtıfScopus5·WoS4·OpenAlex7

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Artuğer, Fırat; Özkaynak, Fatih

Two basic requirements must be met to encrypt data. These requirements are confusion and diffusion properties. In particular, block cipher algorithms are based on a cryptographic component known as substitution-box to provide the need for confusion. Therefore, attack scenarios generally focus on this cryptographic component. There are alternative design approaches for substitution-box design. It is known that each design approach has several advantages and disadvantages. In this study, an alternative method is proposed to address the problems of the substitution-box design approach based on random selection. The success of the proposed method has been tested in three different scenarios. Analysis results for these three scenarios showed that generated substitution-box provides performance increase for nonlinearity criterion from s-box design criteria. Successful results achieved; It points out that improvement cryptographic components can be used in a variety of practical applications such as block ciphers, masks to prevent side-channel attacks, random number generators, and image encryption algorithms.

AtıfScopus29·WoS25·OpenAlex35

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Artuğer, Fırat; Özkaynak, Fatih

What makes artificial intelligence techniques so remarkable in the field of computer science is undoubtedly their success in producing effective solutions to difficult computational problems. In particular, metaheuristic optimization algorithms are a unique example of using artificial intelligence techniques to generate approximate solutions to problems that cannot be solved in polynomial time, called NP. Obtaining a substitution box (s-box) structure that will satisfy the desired requirements in cryptography is an example of these NP problems. In the literature, it is a hot topic to optimize the s-box structures obtained from chaotic entropy sources with heuristic algorithms to improve their cryptographic properties. The study with the highest nonlinearity value (110.25) based on optimization algorithms to date has been published in 2020. In this study, a method with a higher nonlinearity value than the algorithms previously proposed in the literature is developed. It has been shown that the nonlinearity value can be increased to 111.75. These results will be a basis for new research on the chaos-based s-box literature and will motivate new studies to develop alternative optimization algorithms in the future to obtain s-box structures based on the random selection equivalent to the AES s-box.

AtıfScopus47·WoS35·OpenAlex49

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Artuğer, Fırat; Özkaynak, Fatih

In today's digital society, new design alternatives are needed for substitution box structures, which has critical importance in developing secure information systems that are resistant to algebraic and application attacks, as new attacks negatively affect designs based on mathematical transformations. Although random selection-based substitution box structures are a good alternative against algebraic and application attacks, the low value of nonlinearity criterion is an important problem. Solution suggestions using optimization algorithms have been proposed to address this problem. “Information Sciences 523 (2020) 152–166” is the study that reached the highest nonlinearity value based on optimization algorithms to date. However, the high computational costs of optimization algorithms are another challenge that must be overcome. In this study, it has been shown that the nonlinearity values ​​of random (chaotic) selection substitution box structures can be improved as much as mathematically based designs by using a method that is too simple to compare with optimization algorithms. It has been shown that the nonlinearity value can be improved up to 110 for random selection-based substitution box designs. Although this nonlinearity value is the highest achievable value in the literature based on the random selection principle, the fact that it requires only 2×255×255 processes in the worst case has been evaluated as an important success of the proposed method compared to other design approaches. Other advantages of the proposed method are that the improved substitution box structures are resistant to side-channel attacks, simple structure, easy hardware implementation, and successful results in practical applications such as image encryption. It is believed that all these results will be a motivation for new post-processing techniques to be designed in the future for random selection-based substitution box designs.

AtıfScopus42·WoS30·OpenAlex42

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